The Evolutionary Status of WNL Stars

Abstract

We discuss the evolutionary and mass loss implications of recent non-LTE analyses of late WN (WNL) stars in the Galaxy, LMC and M33 using the Wolf-Rayet standard model and address the observed dichotomy of WNL stars discussed by Moffat (1989). Individual subtypes belong to two distinct groups. We find that the single WNL+abs and WN7 stars evolve directly from very massive O stars (60–100 M⊙) with the former intimately related to extreme Of stars and found exclusively in the youngest clusters in our Galaxy. Conversely, the observational properties and chemistries of WN8–10 stars suggest that they are descended from lower initial mass progenitors (~25–60 M⊙). These stars are either dormant LBVs (= WN9–10) or at a phase immediately after this stage (= WN8) although a previous RSG phase cannot be excluded. Included in this subgroup are the LMC and M33 Ofpe/WN9 stars, re-classified as WN9–10 since they appear to be genuine WN stars.